Japanese Patent Application Publication No. 2001-286122 (JP2001-286122A) discloses a linear synchronous motor comprising a stator and a mover that linearly moves relative to the stator. The mover includes a direct drive shaft configured to reciprocate in an axial direction and an array of permanent magnets including a plurality of permanent magnets fixed to the direct drive shaft. The stator includes a plurality of windings and a stator core unit having slots formed therein for receiving the plurality of annular windings. The annular windings are each formed of an annularly wound winding conductor and are disposed so as to surround the direct drive shaft. The stator core unit is constituted from a plurality of stator core divided bodies assembled with each other in the axial direction. The stator core divided bodies are formed by cutting work, and each of the stator core divided bodies includes a magnetic pole portion facing the permanent magnet array of the mover and a cylindrical yoke element which is combined with another stator core divided body so as to constitute a yoke for magnetically connecting the magnetic pole portions. One winding is disposed between two adjacent magnetic pole portions.
In a linear synchronous motor disclosed in Japanese Patent Application Publication No. 2005-328598A (JP2005-328598A), a mover includes two direct drive shafts formed of a magnetic conductive material, and a stator includes two arrays of windings formed to surround the two direct drive shafts. Arrays of permanent magnets fixed to the two direct drive shafts are disposed to be shifted from each other by an electrical angle of 180°. The two arrays of windings are excited, with the two arrays of permanent magnets being shifted by an electrical angle of 180°. In this linear synchronous motor, a magnetic flux flows within the two direct drive shafts formed of the magnetic conductive material. Accordingly, there is no need for the cylindrical yoke element as used in the linear synchronous motor in JP2001-286122A.
In the linear synchronous motor in JP2005-328598A, however, the magnetic flux is flown through the two direct drive shafts and each core. Thus, the magnetic flux may be flown in a locally concentrated state, so that magnetic saturation may occur. Further, a magnetic circuit between the cores is not closed, so that magnetic flux leakage tends to occur. For that reason, even if the two direct drive shafts are used, a thrust force of the linear synchronous motor cannot be sufficiently increased. Further, in the linear synchronous motor in JP2005-328598A, a mover stage for mounting the mover and a base for disposing the stator are provided. Then, the mover stage is slidably supported relative to the base. For that reason, a support structure for supporting the mover relative to the stator becomes extensive, so that the volume occupied by the linear synchronous motor increases.